1. Field of the Invention
The present invention is related to a mask of a lithographic process, a method of manufacturing the mask and a lithographic process by using the mask. More particularly, the present invention relates to a mask of a lithographic process, a method of manufacturing the mask and a lithographic process by using the mask, wherein the mask comprises a layer having a first polarization direction of light and a patterned layer having a second polarization direction of light.
2. Description of Related Art
Conventionally, lithographic and etch process is important in a semiconductor manufacturing process for patterning a film. Generally, in the semiconductor process, a photoresist layer is formed over a film formed on a semiconductor substrate that will be patterned. Next, the photoresist layer is exposed using a mask to transfer a specific pattern on the mask onto the surface of the photoresist layer. After the photoresist layer is trimmed with respect to the specific pattern transferred, the remaining patterned photoresist layer is used as an etching mask layer for etching an underlying film. Finally, after etching the film using the patterned photoresist layer as an etching mask, the patterned photoresist layer is stripped. Thus, the film is patterned using lithographic and etch process described above.
FIG. 1 is a schematic cross-sectional view of a conventional mask. FIG. 2 is a schematic view of a conventional lithographic process. Referring to FIG. 1, the conventional mask 100 includes a transparent glass 102, and a patterned chromium layer 104 formed on the glass. The patterned chromium layer 104 includes a specific pattern that will be transferred onto the photoresist layer 206 shown in FIG. 2. In addition, a patterned chromium dioxide layer 106 may also be formed over the surface of the patterned chromium layer 104 to prevent the reflection of the light used in the lithographic from the surface of the patterned chromium layer 104.
Referring to FIG. 2, a light 212 is adopted for transferring the specific pattern on the mask 100 onto a substrate 202 via a lens 208. A layer 204 to be patterned is formed on the substrate 202, and a photoresist layer 206 is formed on the layer 204. FIG. 3 is a plot of a normalized light intensity generated via a conventional mask. Referring to FIG. 3, the photoresist layer 206 is exposed by a light 304 illuminated thereon. The light 304 is formed by illuminating the light 212 via a specific pattern 302 (i.e., constructed by the patterned chromium dioxide layer 106 formed on the mask 100) and focusing the transmitted light 216a, 216b via the lens 208. In general, the resolution of line width or critical dimension formed in the layer 204 after etch process is dependent on the resolution of the light 304. It is noted that the resolution of the light 304 generated by the conventional mask 100 is poor since the normalized light intensity (i.e., the image contrast) of the light 304 is relatively small. The reason why the normalized light intensity of the light 304 is small will be described hereinafter. The light 212 includes two directions of polarization, one has traverse electric mode TE212 (illustrated in a direction perpendicular to the plane) and the other has traverse magnetic mode TM212 (illustrated perpendicular to the light 212 and the TE212). The light 304 is generated from the transmitted light 216a, 216b, however, the resolution of the light 304 is reduced by the unexpected polarizations TM216a and TM216b. In general, the polarizations TM216a and TM216b are almost perpendicular to each other, which make low image contrast of optical interference of the combination of TM216a and TM216b. 
Recently, as the semiconductor process advances, the line width or the critical dimension of the semiconductor structure is being minimized rapidly to increase the integration of the semiconductor device. However, with the reduction of the line width, a variety of problems arise in a conventional lithographic and etch process. In general, reducing the wavelength of light 212 may improve the resolution of line width or critical dimension. For example, pattern with resolution of line/space dimension of about 0.5 μm may be formed by using i-line laser with a wavelength of 365 nm. Furthermore, pattern with resolution of line/space dimension of about 0.25 μm may be formed by using KrF laser having a wavelength of 248 nm or ArF laser having a wavelength of 193 nm. However, as the line width or critical dimension of the recently semiconductor process is reduced to 100 nm, 90 nm, 60 nm or less, to reduce the wavelength of the light 212 will make the lithographic process more complicated and increase the cost drastically.
In addition, as the pitch of patterns on mask 100 (i.e., proportional to the intervals between the patterned chromium layers 104) reduces, the numerical aperture (NA) of the lens 208 used in the lithographic process has to be increased to enhance the resolution of the line width or critical dimension. However, as the numerical aperture (NA) increases, the depth of focus (DOF) in the photoresist layer 206 is reduced, i.e., the depth of the exposed pattern in the photoresist layer 206 may not enough. Furthermore, the image contrast of the exposed pattern on the photoresist layer 206 may be degraded and the process window of the lithographic process and etch process may decrease. In addition, chromium is a contamination that may pollute the environment. Accordingly, to improve the conventional lithographic process and the mask using thereof, and to develop a contamination free mask is highly desired.